Ernie Ball .012 Plain Steel String - Single StringBrand Ernie BallString Gauge Extra HeavyInstrument Acoustic GuitarString Material Type Nickel SteelErnie Ball Model#1012Ernie Ball Plain Steel Electric or Acoustic Guitar Strings are made of specially tempered tin plated high carbon steel used on electric and acoustic guitars. Ernie Ball revolutionized the market by offering Custom-Gauge single string options allowing guitarists to create personalized string sets.